Re: [APD] aeration & a planted tank

["S. Hieber" <shieber at yahoo_com>]

--- Raj <ggrk at blr_vsnl.net.in> wrote:

> 
>          Basically aeration causes the water to be lifted
> from the lower 
> levels to the surface. 

Airstones yes. Waterfalls (e.g., from a hang on filter),
biowheels, water pumps that provide good circulation yield
good air-water exposure but but in a slightly diff way.

> I haven't done the math but I
> don't think that a 
> rising column of air bubbles will present a significant
> surface area of 
> water to air to result in actual aeration. 

Well, probably depends on the amount and size of air
bubbles ;-)

> Any form of
> agitation should 
> help the gas exchange.

Circulating the water so that more of it comes in contact
with the air will do this. Surface agitation markedly
increases the gas exchange.

>          Agitation is beneficial in the day too.. the
> plants deplete the 
> CO2 under good lighting and good gas exchange will
> replenish the CO2 thus 
> improving the plant growth.

This probably depends on several factors. Some folks have
measured CO2 levels higher than they would be from mere
water & air gas exchange. Perhaps CO2 from the fish
contributes.

The amount of CO2 in a tank without injected CO2 is pretty
low, so even doubling it (or halving it) probably doesn't
have much impact on plant growth.

> 
>          In a CO2 added tank the plant growth is much
> faster than in an 
> water circulated, surface agitated or aerated tank. I
> have equally good 
> results in both types.

It's not harmful to agitate the water, it simply causes
injected CO2 to be shed faster, increasing one's CO2 costs.
For example, I've tried several diff set-ups involving a
sump but they all result in my having to supply twice as
much CO2 gas to maintain 25ppm CO2 in the water compared to
using a canister filter. The increased cost if several
dollars per month, which I accept for the convenience that
the sump system offers.

>          OTOH, I hate to see fish gasping in the mornings
> in a densely 
> planted tank with hyperactive plants (CO2 fed). I have
> noticed this 
> recently in a non CO2 tank.. time to thin the plants?
> There must be a 
> balance between the plant density & fish population,
> difficult to estimate 
> in my opinion.
> 
>          Anyone done the math on the surface area of a
> rising column of air 
> bubbles?

Don't know where the math is but you can move a heck of a
lot more water with a realtively small wattage water pump
than a with a bubble stream from a comparable wattage air
pump.

I am curious about your low O2 levels despite the abundant
presence of plants. Certainly, if your fish are trying to
take in water at the surface ("gasping"), this suggests
that more water flow (air-water exposure) could be useful
to reducing stress on the fish. Also more water flow or
perhaps an improved water flow might help move nutrients to
the plant surfaces to increase their ability to do their
thing (take in nutrients, photosynthesize, etc.) and boost
O2 levels enough in the day to last through the night.

My main complaint about airstones in aquaria, and it's
strictly a personal one, is that a bubble stream is so
artifical looking. so I'd rather use water flow pumps
(filters, powerheads, etc.) to move water.

Scott H.

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